VIRAL AND RICKEITSIAL DISEASES

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Abstract
INTRODUCTION IT WILL not be possible to cover exhaustively the field of virus and rickettsial diseases in this brief summary. The growth and basic properties of viruses and rickettsiae as well as the pathogenesis of diseases due to these agents will be reviewed in outline form. Epidemiology and immunity and current opinion on prophylaxis and therapy will be discussed. Finally, we will consider some recent developments and speculate a bit on what the future may offer. It is hoped that some of the more basic material presented, although admittedly elementary, will help to orient the reader. An understanding of some of the procedures conducted in the virus laboratory may make the physician aware not only of what can be done to help diagnostically, but also what cannot be done. FUNDAMENTAL INFORMATION CONCERNING PROPERTIES OF VIRUSES AND RICKETTSIAE A) Size 1) Rickettsiae are large enough to be seen with the light microscope and do not pass through porcelain filters. The rickettsia of Q fever does have filtrable form. 2) Viruses vary tremendously as to size. Some are highly complicated organisms (e.g., vaccinia), others such as tobacco mosaic virus, are apparently large protein molecules. Psittacosis and related organisms occupy intermediate position between rickettsiae and true viruses. B) Culture No virus or rickettsia has ever been propagated except in the presence of living cells. C) Life Cycle Most of time available information concerning infection of time cell and multiplication of viruses is derived from studies with bacterial viruses (bacteriophage). This may or may not be fully applicable to animal viruses but the cycle is represented below:

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